Nikkei Sesame-Seared Ahi Tuna with Yuzu-Rocoto Chimichurri

Instructions

1. 1

   Preheat your oven to 425°F (220°C). Bring a medium pot of generously salted water to a boil for the potatoes.

   10 min

   Tip: Always salt your potato water until it tastes like the ocean. It's your only chance to season the inside of the potato.

2. 2

   Add 1 lb fingerling potatoes to the boiling water. Cook until just fork-tender, which should take about 15 minutes depending on their size.

   15 min

   Tip: Don't overboil them or they will disintegrate when smashed. You want them just yielding.

3. 3

   While the potatoes boil, let's talk acid balancing and build the chimichurri. In a bowl, combine 1/2 cup fresh cilantro, 1/4 cup fresh shiso leaves, 2 scallions, and 1 clove garlic. Stir in 1 tbsp rocoto paste, 2 tbsp yuzu juice, and 1 tbsp rice vinegar. The sharp, floral yuzu and mellow, sweet rice vinegar create a dual-acid structure. Whisk in 1/4 cup extra virgin olive oil and 1 tbsp toasted sesame oil. Let this sit so the acids lightly 'cook' the raw garlic and herbs.

   10 min

   Tip: Letting the chimichurri macerate is critical. The acid softens the harshness of the raw garlic and blooms the capsaicin in the rocoto.

4. 4

   Drain the cooked potatoes and place them on a heavy baking sheet. Using the bottom of a heavy glass, gently smash each potato until flattened but still intact. Drizzle with 2 tbsp neutral oil, season with salt, and roast in the oven until deeply golden and crispy.

   20 min

   Tip: Let the potatoes steam off for a minute after draining before smashing—the drier they are, the crispier they get.

5. 5

   While the potatoes roast, prep the tuna. Pat the 1.5 lbs sushi-grade ahi tuna saku block perfectly dry with paper towels. Lightly brush all sides with 1 tbsp soy sauce—this acts as an umami-rich glue. Pour the 1/4 cup mixed black and white sesame seeds onto a plate and press the tuna into the seeds to coat evenly on all sides.

   5 min

   Tip: Drying the fish first ensures the soy sauce coats evenly and doesn't just run off.

6. 6

   Heat the remaining 1 tbsp neutral oil in a carbon steel or cast-iron skillet over screaming high heat. Once the oil begins to smoke lightly, add the crusted tuna. Sear for exactly 30 seconds per side. Remove immediately to a cutting board.

   3 min

   Tip: Do not walk away. You want a millimeter of cooked white meat and a completely rare, ruby-red center.

7. 7

   Now for the precision slicing. Using your sharpest, longest knife (a Yanagiba is ideal, but a sharp chef's knife works), find the grain of the tuna. You must cut against it. Angle your blade at 45 degrees and, using one long, smooth pulling motion, slice the tuna exactly 1/4-inch thick. Do not saw back and forth.

   2 min

   Tip: Cutting exactly 1/4-inch thick on a bias maximizes the surface area of the fish. This is crucial because it gives our acidic chimichurri more area to cling to, perfectly balancing the bite.

8. 8

   To plate, lay down a bed of the crispy smashed potatoes. Fan out your precision-sliced tuna over the top. Spoon the macerated yuzu-rocoto chimichurri generously over the fish, ensuring the oils pool slightly on the plate. Finish with 1 tsp flaky sea salt.

   2 min

   Tip: Plate while the potatoes are hot and the tuna is cool. That temperature contrast is a beautiful thing.